The invention relates to methods for use in joining tubular members to another member, such as a tubeplate for example by expansion of the tubular member; and to members so joined.
The expression tubeplate comprises a plate or other wall whether it is a wall of a header, a drum or some other component.
It has already been proposed in U.S. Pat. No. 4,006,619 to expand a tube by axially compressing an annular body of rubber or other elastomeric material within the tube by mechanically applied force so as to produce radial expansion of the body. In that method the annular body is supported at its ends by respective annular arrays of separate metal segments.
In that method, the tube is expanded only outside the tube-plate and the tubeplate is not stressed beyond its elastic limit by the expansion of the body of elastomeric material.
It has also been proposed in U.S. Pat. No. 4,068,372 to expand a tube within a tubeplate by axially compressing an annular body of elastomeric material within the tube so as to produce radial expansion of the body.
In that proposal, the annular body is supported at its ends by relatively hard seal rings of synthetic plastic material. In that proposal the length of the unstressed body of elastomeric material is less than the thickness of the tubeplate and the tube is expanded over a portion of its length within the tubeplate which portion is considerably less than the thickness of the tubeplate.
In the method proposed in U.S. Pat. No. 4,068,372, the tubeplate is not stressed across its full thickness by expansion of the tube and for optimum tube holding force and watertightness, it is proposed that the tube be expanded into annular grooves formed in the wall of the aperture in the tubeplate.
It has been proposed in British patent specification Nos. 1,534,107 and 1,543,524 to expand a tube within a tubeplate by pressurised hydraulic fluid acting directly on the inside of the tube. In that method it is proposed to expand the tubeplate by application of pressure greater than that value at which the unobstructed elastic recoveries of the tubeplate and the tube are equal. That is, after the expansion has been completed and the pressure is relieved, the tubeplate grips the tube tightly because of the residual stress in the tubeplate.
In the method proposed in British specification Nos. 1,534,107 and 1,543,524, pressure is applied to the tube over a portion of its length which is less than the thickness of the tubeplate.
It has been proposed in U.K. patent specification No. 1,489,719 to expand a tube within a tubeplate by applying hydraulic pressure over a portion of the length of the tube which is less than the thickness of the tubeplate and then to push the non-expanded part of the tube out of the tubeplate by mechanically rolling the tube internally in that expanded portion.
In using any of the methods referred to above, and as explained in U.K. specification No. 1,489,719, a difficulty arises in trying to ensure that the tube is expanded properly into contact with the tubeplate over the full thickness of the tubeplate; or alternatively, a difficulty arises in achieving any or adequate residual stress in the tubeplate.
Using such methods, where inadequate stress in the tubeplate is achieved or the tube is expanded into contact over less than the full thickness of the tubeplate, holding strength is lost and crevices may occurs at which corrosion may arise.